guarantee that bits is non-null once resize has been called

src/main/java/com/zaxxer/sparsebits/SparseBitSet.java

@@ -1714,7 +1714,7 @@ protected final void resize(int index)
             newSize = MAX_LENGTH1;
         final int aLength1 = (bits != null ? bits.length : 0);
 
-        if (newSize != aLength1)
+        if (newSize != aLength1 || bits == null)
         { // only if the size needs to be changed
             final long[][][] temp = new long[newSize][][]; //  Get the new array
             if (aLength1 != 0)

src/test/java/com/zaxxer/sparsebits/InitWithZeroTest.java

@@ -0,0 +1,44 @@
+package com.zaxxer.sparsebits;
+
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+
+public class InitWithZeroTest {
+    private SparseBitSet bitset;
+
+    @Before
+    public void setup() {
+        bitset = new SparseBitSet(0);
+    }
+
+    @Test
+    public void testPreviousSetBit() {
+        Assert.assertEquals(-1, bitset.previousSetBit(0));
+    }
+
+    @Test
+    public void testPreviousClearBit() {
+        Assert.assertEquals(0, bitset.previousClearBit(0));
+    }
+
+    @Test
+    public void testNextSetBit() {
+        Assert.assertEquals(-1, bitset.nextSetBit(0));
+    }
+
+    @Test
+    public void testNextClearBit() {
+        Assert.assertEquals(0, bitset.nextClearBit(0));
+    }
+
+    @Test
+    public void testClone() {
+        Assert.assertEquals(-1, bitset.clone().nextSetBit(0));
+    }
+
+    @Test
+    public void testAnd() {
+        bitset.and(new SparseBitSet());
+    }
+}